共查询到20条相似文献，搜索用时 31 毫秒
1.
G.M.L. Sommerman 《Journal of The Franklin Institute》1935,219(4):433-458
The presence of maxima in the power factor-frequency and power factor-temperature curves of dielectrics has been explained by the Maxwell inhomogeneity theory and the Debye theory of polar molecular orientation. In order to ascertain the true cause of these maxima, a study has been made of the power factor of an essentially non-polar material with and without polar materials in dilute solution over extended ranges of frequency, 65 to 7.2 × 106 c.p.s., and temperature, 2.9° C. to 90° C.The non-polar solvent is a mixture of paraffins having a pour point at 55° C. Small power factor maxima, 0.0003 in value, shifting over the audio frequency range with temperature variation, are observed for this solvent alone. Adding 3 per cent. phenol gives rise to molecular orientation maxima restricted largely to frequencies above 107 c.p.s. At the lower temperatures, these maxima are greatly broadened, so that there is apparently a small contribution at power frequencies. Adding 10 per cent. stearic acid gives similar results. The failure of these maxima to shift to lower frequencies at the lower temperatures is due to the failure of the inner viscosity to increase very much in the solid state. The variation of the inner viscosity is calculated from the reciprocals of the short time conductivities since the degree of ionic dissociation is found to be essentially independent of temperature. The viscosity may be regarded as a function of particle size and varies within the medium. Where power factor maxima shift with essentially undiminished magnitude over a wide frequency range at ordinary temperatures, such as those observed here in the solvent above, it is believed that the cause is the orientation of associated or polymerized polar aggregates of such size as to be affected by the larger viscosity changes approaching the macroscopic.In the solid and amorphous states, the limited motion of ions leads to an ionic polarization as indicated by absorption curves of relatively large time constants and by high power factors in the low frequency range. The addition of organic acids greatly increases these effects and also increases the final conductivity. The true short time conductivity is largely caused by almost completely dissociated inorganic material. 相似文献
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The relation between particle size and the degree of polarization of the Tyndall beam created by suspension of non-uniform particulate substances was investigated for three materials (silica, granite, and calcite) ranging in size from one to fifty microns. The degree of polarization was found to be a function of the arithmetic mean diameter of the material. The optical property of birefringence was also found to be a determining factor although its effect was not studied quantitatively. It is shown that by combining the equation expressing the relation between particle size and strength of Tyndall beam with the mathematical relation between degree of polarization and particle size, an indirect method of obtaining a complete definition of particle size is given. Particle size values calculated from observed Tyndall readings and measurements of polarization were found to be within approximately ten per cent. of observed values. 相似文献
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1961-2012年云南省极端气温时空演变规律研究 总被引：2，自引：0，他引：2
利用云南省122个气象观测站1961-2012年逐月极值气温资料,采用线性趋势分析等方法分析1961-2012年云南省四季和年极端气温的变化趋势特征。结果表明:低纬高原地区年平均最高(最低)气温及四季最高(最低)气温的空间分布呈现北低南高的形式,整体上从滇西北向南随纬度的降低而增加,表现出明显的地区差异,最高(最低)气温的高值区域主要分布在河谷地区、云南南部地区,最高气温和最低气温的分布特征不仅受复杂地形的影响,而且还与观测站的海拔高度有关。最高(最低)气温低值区域主要分布在滇西北、滇东北;云南年平均最高气温与夏、秋、冬季最高气温的变化趋势基本相似,春季最高(最低)气温的变化具有明显的区域特征。除局部地区有降温外,升温趋势是最大的特点,升温最快的区域在滇西北。云南最高气温和最低气温的变化均呈明显的增温趋势,而最低气温的变化速度比最高气温的升温幅度快,说明云南的冷事件在减少,暖事件在增多。最高气温和最低气温的突变时间分别发生在2001年和1993年,最高气温的极大值出现在2010年,而最低气温的最大值也发生在2010年。不同气候类型代表站极端气温具有年代际和年际变化周期;极端气温发生的突变时间不同,而部分代表站的极端气温并未发生突变。 相似文献
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论专利制度对创新的激励 总被引：10，自引：1，他引：9
技术创新是从发明创造到科技成果实现商业化的过程。西方专利制度发展史显示了专利制度对技术创新和经济发展的巨大推动作用。专利制度能够实现对技术创新激励作用的关键在于它是关于产权界定的制度。专利权是私人财产权,也是人们对其发明创造享有的独占权。对这种产权进行界定将大大激发人们的创新活力。因此,专利制度是一种最有效的创新机制。作者认为,在依法保护专利同时,应对这种独占权给予必要的限制,以维护社会公共利益,保持社会恒久的创新能力。 相似文献
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Joseph Samuel Hepburn 《Journal of The Franklin Institute》1915,179(5):581-585
The power to survive prolonged exposure to low temperatures is possessed by various enzymes, including those producing hydrolysis of fats, of carbohydrates, and of proteins, those concerned in biochemical oxidations and reductions, the clotting enzymes and that of alcoholic fermentation. The enzymes retained their catalytic power after exposure, either in situ or in solution in vitro, to temperatures varying from a few degrees above 0° C. to the temperature of liquid air (?180° to ?191° C.). The shortest periods of holding, invariably less that one day and usually less than one hour, were at the temperature of liquid air. The longest period of holding was eighty-nine months at a temperature of ?9.4° to ?12.2° C.The activity of certain of these enzymes, including rennin, zymase, and those hydrolyzing fats, carbohydrates, and proteins, has been studied at low temperatures, varying from that of an ice-box to one of ?9° to ?12° C. While the enzymes produced autolytic digestion or acted on artificial media at these temperatures, the velocity of the reaction was always lessened to a considerable degree. 相似文献
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Karthiga Panneerselvam Martin E. Lynge Camilla Frich Riber Sofia Mena-Hernando Anton A. A. Smith Kenneth N. Goldie Alexander N. Zelikin Brigitte St?dler 《Biomicrofluidics》2015,9(5)
Recently, the combination of lipids and block copolymers has become an alternative to liposomes and polymersomes as nano-sized drug carriers. We synthesize novel block copolymers consisting of poly(cholesteryl acrylate) as the hydrophobic core and poly(N-isopropylacrylamide) (PNIPAAm) as the hydrophilic extensions. Their successful phospholipid-assisted assembly into vesicles is demonstrated using the evaporation-hydration method. The preserved thermo-responsive property of the lipid-polymer hybrids is shown by a temperature dependent adsorption behaviour of the vesicles to poly(l lysine) coated surfaces. As expected, the vesicle adsorption is found to be higher at elevated temperatures. The cellular uptake efficiency of hybrids is assessed using macrophages with applied shear stress. The amount of adhering macrophages is affected by the time and level of applied shear stress. Further, it is found that shorter PNIPAAm extensions lead to higher uptake of the assemblies by the macrophages with applied shear stress. No inherent cytotoxicity is observed at the tested conditions. Taken together, this first example of responsive lipid-polymer hybrids, and their positive biological evaluation makes them promising nano-sized drug carrier candidates. 相似文献
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文章介绍了太阳系和太阳系外行星冰冻圈。太阳系各行星和卫星的表面温度差异很大,它们的冰冻圈发育各不相同。水星和月球的两极陨石坑的永久阴影区中可能有水冰存在。金星太热,表面既没有液态水,也不可能有水冰存在。火星两极存在永久性冰帽,包括水冰和干冰(固态CO2)。在太阳系雪线之外,存在很多冰卫星和富含水的矮行星,它们的主要是由水冰组成的;在极低的温度下,水冰甚至比地球上的岩石还要坚硬,并成为这些星体的壳层。除了水冰,其他易挥发组分如CO2、CH4、N2、CO等在极低温度下都会凝固为冰,形成不同于水冰的冰冻圈。因此,行星冰冻圈具有与地球冰冻圈迥然不同的丰富多样性。对行星冰冻圈的研究有助于我们扩大视野,更深入地理解地球冰冻圈,也将有助于我们理解太阳系的形成、地球水分的来源、地球深时古气候环境和生命演化,以及开展未来的系外生命探测。 相似文献
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文章以转基因作物为例讨论了转基因的生物安全。转基因作物在带来经济利益的同时,其对环境和健康的安全性也成为研究的焦点。从目前转基因生物安全主要争论的内容出发,包括转基因逃逸及其生态学后果、对非靶标生物影响、害虫的抗性进化等方面,结合相关的案例综合介绍了近年来的主要进展和存在的问题。对那些科技界争论较多,引起强烈社会反响事件的起因和主要结论进行了客观的评述,以期为进一步的科学研究提供依据。根据中国的实际情况,考虑到生物安全的要求,为保护生物多样性的可持续利用,提出相关的建议和对策:(1)以生物安全相关的科学问题为主,具体的目标生物为辅,开展系统的实验研究;(2)加强生物安全的监测与监管,鉴别重要生态功能区和生态脆弱区,适当设立转基因保护区,禁止种植转基因作物;(3)重视公众知情权,不仅宣传转基因生物带来的惠益,也应告知其风险及管控措施,促进公众的理解和认可。 相似文献
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W.H. Ingram 《Journal of The Franklin Institute》1925,200(6):757-765
The equations connecting the winding current and diaphragm motion of a telephone receiver under impressed simple harmonic electromotive and mechanical forces are formulated under: (I) The Maxwell flux theory; (2) the magnetizing-winding theory; (3) the Ampèrean resistanceless fixed molecular circuit theory of permanent magnetism; and (4) a general molecular orbital theory of ferromagnetism. On the latter theory it is found that the coupling coefficients M and N in the equations in question are in general different, in counter-distinction to the other three theories as hitherto formulated. The flux theory is shown not to be inconsistent with this result when certain dynamical phase relations are introduced into the static flux-magnetomotive force formula (Ohm's Law analog) always employed in this theory. The Ampèrean rigid circuit theory is criticized as an inadequate dynamical representation of ferromagnetism. The magnetizing-winding theory (dynamical) is reproduced in slightly generalized form. 相似文献
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BackgroundRemoval of dyes from wastewater by microorganisms through adsorption, degradation, or accumulation has been investigated. Biological methods used for dye treatment are generally always effective and environmentally friendly. In this study, biosorption of the Fast Black K salt azo dye by the bacterium Rhodopseudomonas palustris 51ATA was studied spectrophotometrically, at various pH (2–10), temperatures (25°C, 35°C, and 45°C) and dye concentrations (25–400 mg L-1).ResultsThe bacterial strain showed extremely good dye-removing potential at various dye concentrations. IR studies at different temperatures showed that the dye was adsorbed on the bacterial surface at lower temperatures. Characteristics of the adsorption process were investigated by Scatchard analysis at 25°C and 35°C. Scatchard analysis of the equilibrium binding data for the dye on this bacterium gave rise to linear plots, indicating that the Langmuir model could be applied. The regression coefficients obtained for the dye from the Freundlich and Langmuir models were significant and divergence from the Scatchard plot was observed.ConclusionThe adsorption behavior of the dye on this bacterium was expressed by the Langmuir, Freundlich, and Temkin isotherms. The adsorption data with respect to various temperatures provided an excellent fit to the Freundlich isotherm. However, when the Langmuir and Temkin isotherm models were applied to these data, a good fit was only obtained for the dye at lower temperatures, thus indicating that the biosorption ability of R. palustris 51ATA is dependent on temperature, pH, and dye concentration.How to cite: Öztürk A, Bayol E, Abdullah MI. Characterization of the biosorption of fast black azo dye K salt by the bacterium Rhodopseudomonas palustris 51ATA strain. Electron J Biotechnol 2020;46. https://doi.org/10.1016/j.ejbt.2020.05.002. 相似文献
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从五个方面论述了研究生教育中的学术规范与知识产权关系研究。(1)研究生教育中常见学术失范与其所侵犯的知识产权;(2)造成研究生学术失范、侵犯他人知识产权屡禁不止的原因;(3)严格的学术规范是尊重他人知识产权的前提;(4)加强知识产权教育,会促进研究生自觉遵守已有的学术规范;(5)学术规范与知识产权保护二者相辅相成。 相似文献
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Martin A. Pomerantz 《Journal of The Franklin Institute》1946,241(6):415-433
The secondary electron emission from alkaline-earth oxide-coated cathodes has been investigated under both continuous and pulsed bombardment. Various factors affecting the yield, such as dependence upon primary voltage, collecting voltage, temperature, time, and angle of incidence, are noted, and the present state of the theory is discussed.Experiments have been performed with three types of apparatus. Yield vs. Energy data reveal values of δ of 4–7 at room temperature, with a more or less flat maximum at approximately 1,000 volts primary energy.The yield increases with temperature in an exponential manner, and plots of log Δδ (i.e. δK° ? δ300°K) vs. 1/T give straight lines. Values of Q1 between 0.9 – 1.5 eV. are generally indicated, and from extrapolation of these curves, yields exceeding 100 at 850° C. are deduced. The secondary emission depends upon the degree of activation, and increases with enhancement of the thermionic emission characteristics. Short-time effects such as growth or decay of secondary current after the onset of primary bombardment or persistence after the cessation of bombardment have not been observed, and values of yield obtained by pulsed methods are in accord with those obtained under D.C. conditions. Tail phenomena reported by J. B. Johnson and interpreted as “enhanced thermionic emission” from oxidecoated cathodes become manifest only under experimental conditions characterized by certain space-charge effects, and have been effectively simulated by bombarding a tantalum target adjacent to an electron-emitting tungsten filament. Various measurements of the energy distribution of secondary electrons as a function of primary voltage and temperature have been obtained. It was observed that the average energy of the secondary electrons decreases with temperature at a rate which more than compensates for the increase in the number of secondaries emitted per incident primary. The mechanism of the observed dependence of yield upon temperature is not well understood. Various alternative explanations are discussed and, in the light of the present state of our knowledge, regarded as untenable. 相似文献
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Dynamical systems in the real world are always subject to various disturbances. This paper studies the dynamics of linear delayed systems with decaying disturbances, both discrete- and continuous-time cases are considered. It is first shown that if an unforced linear system is exponentially stable, then the disturbed system has a dynamical property like exponential stability provided that the disturbance decays at an exponential rate, and has a dynamical property like asymptotic stability provided that the disturbance asymptotically approaches zero. These results are then applied to block triangular systems in the presence of time-varying delays, leading to criteria for checking the stability properties of this class of systems by considering diagonal blocks of system matrices. Particularly, a block triangular system is exponentially stable if and only if each system described by the diagonal blocks of system matrices is exponentially stable. Finally, a numerical example is presented to illustrate the theoretical results. 相似文献
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从知识产权立法保护和执法保护两个方面构建了中国知识产权保护强度,并运用1985——2010年的实际数据进行了计算。结果显示中国知识产权保护强度指数从1.156上升到2.980。运用Chow检验发现在2001年(中国加入TRIPS协议的当年)中国知识产权保护强度发生了结构断点。进一步的Granger因果关系检验表明经济发展水平和技术创新能力是促进我国知识产权保护强度的因素,但受总体经济发展水平的影响,我国的知识产权保护还没有有效促进经济发展和技术创新能力提升。 相似文献
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聚焦高校教师群体,探讨内外部创业环境对兼职创业行为的影响.借助数理模型和实证分析,解析各类创业资源对高校教师创新驱动型兼职创业活动的影响机制,并探究创业自我效能感在创业资源和高校教师创新驱动型兼职创业活动之间的中介作用.研究发现:(1)现阶段我国高校兼职创业者呈现较明显的创业群体和创业模式特征;(2)创业时间资源和资产... 相似文献
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大体积混凝土的浇筑时混凝土水化热温度变化影响在于冷凝大,容易导致高温,干缩裂缝会损伤混凝土结构,因此有必要采取一些措施来控制温度的检测。我们项目针对1#和2#桥梁混凝土的浇筑过程主塔墩和浇注温度变化的温度控制和跟踪执行,并控制浇注温度在一系列温度检测项目的实施过程中采取的相应措施。 相似文献